/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory;

import org.springframework.beans.BeansException;

/**
 * ObjectFactory则只是一个普通的对象工厂接口,
 * 在查看AbstractBeanFacotry的doGetBean(…) 部分的源码时，可以看到spring对ObjectFactory的应用之一就是，
 * 将创建对象的步骤封装到ObjectFactory中 交给自定义的Scope来选择是否需要创建对象来灵活的实现scope
 * @see org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#getSingleton(java.lang.String, org.springframework.beans.factory.ObjectFactory)
 *
 * 区别：
 * FactoryBean的着重于自定义创建对象过程，由BeanFactory通过FactoryBean来获取目标对象，而如果是isSingleton返回true的话，spring会利用单例缓存来缓存通过FactoryBean创建的对象。
 *
 * 而ObjectFactory就是一个普通的工厂对象接口，对于spring在doGetBean处的使用时，在于创建对象的过程由框架通过ObjectFactory定义，
 * 而创建的时机交给拓展接口Scope，除此之外ObjectFactory就是一个普通的接口
 * 此外在将给依赖注入列表注册一个ObjectFactory类型的对象，
 * 在注入过程中会调用objectFactory.getObject()来创建目标对象注入进去。
 * （如beanFactory.registerResolvableDependency(HttpSession.class, new SessionObjectFactory());）
 *
 *
 * Defines a factory which can return an Object instance
 * (possibly shared or independent) when invoked.
 *
 * <p>This interface is typically used to encapsulate a generic factory which
 * returns a new instance (prototype) of some target object on each invocation.
 *
 * <p>This interface is similar to {@link FactoryBean}, but implementations
 * of the latter are normally meant to be defined as SPI instances in a
 * {@link BeanFactory}, while implementations of this class are normally meant
 * to be fed as an API to other beans (through injection). As such, the
 * {@code getObject()} method has different exception handling behavior.
 *
 * @author Colin Sampaleanu
 * @since 1.0.2
 * @param <T> the object type
 * @see FactoryBean
 */
@FunctionalInterface
public interface ObjectFactory<T> {

	/**
	 * Return an instance (possibly shared or independent)
	 * of the object managed by this factory.
	 * @return the resulting instance
	 * @throws BeansException in case of creation errors
	 */
	T getObject() throws BeansException;

}
